The aim of this research is to examine the effects of aging on secretory IgA antibody responses. We propose to use the rat as a model system to study salivary IgA responses at the humoral and cellular level. Levels of IgA in saliva of weaning, adult, mid-life and aged rats will be determined, as well as the cellular composition (T, B, macrophage, and immunoglobulin-containing cells) of lymphoid and secretory tissues associated with salivary secretions. The ability of normal and aged rats to manifest a salivary IgA response to T-dependent (DNPBGG) and T-independent (DNP-Ficoll, DNP-POL) antigens will be assessed using an enzyme-linked immunosorbent assay (ELISA). The response to these antigens will help elucidate the cellular defect resulting in decreased secretory IgA production. Furthermore, to probe T cell capabilities in the aged rats, carrier specific cell cooperation will be examined with hapten-carrier conjugate antigens. Finally, T cell subpopulation distribution studies in IgA precursor tissues (Peyer's patch) and T cell reconstitution experiments will be used to delineate the cellular mechanism leading to the defect in secretaroy IgA responses. The results should enable a better understanding of aging effects on mucosal immune defenses and may indicate modes of reversing the deficiencies.